Fuel imbalance

[Hamilton 0]

I was flying on my 737-900NGX when i noticed a huge fuel imbalance and i tried to correct it by opening the fuel cross feed , but nothing happened, so, what´s the proper way to correct it.

 

Hamilton.

[Chrjs 61]

After opening the cross feed valve did you shut off the Fuel Pump of the affected side?

[Hamilton 0]

No, am I supposed to?

[serviceceiling 135]

Yes, the 737 is not an Airbus.

[VIPERGTSR01 22]

How did you get a imbalance like that anyway? Fuel leak?

[VLJ510 16]

QRH is your friend.

[coa1117 53]

Had the same thing in a -900 a couple of hours into a long flight: SFO-PHL. All failures disabled and the tanks were balanced at t/o. Opening the X-feed and killing the affected pump worked OK, but with a 500 LB difference it took some time. The problem didn't happen again during the flight. Never did figure out the cause.

[rsvit 16]

Opening the X-feed and killing the affected pump worked OK, but with a 500 LB difference it took some time. The problem didn't happen again during the flight.

 

In which tank it was more fuel? On NGX I usually get imbalance if I use APU for a long time or if I leave some fuel in a main tank and fuel scavange pump move it to main tank #1.

[kevinh 409]

Never did figure out the cause.

Did you leave the APU running? That'll certainly give you a fuel imbalance.

[davierosoft 13]

In the picture the tank 1 is lower, much lower, probably due to long APU usage (but this is a serious imbalance, I don't think it is related only to the apu)

[Oliver Branaschky 2]

I've seen this only once so far: while using time acceleration, which I haven't done ever since. Maybe that was a reason, I don't know...

 

 

Oliver Branaschky

[coa1117 53]

Did you leave the APU running? That'll certainly give you a fuel imbalance.

 

The APU definitely wasn't running in-flight, and the imbalance, as I now recall, was ~800 lbs. I could be wrong, but I think I've read that the NG's APU burns approximately 4 lbs/minute. I always use the GPU at the gate, fire-up the APU just before PB, and shut it down immediately after two good engine starts. So, no, APU usage wouldn't account for the size of the imbalance.

 

Someone else asked which tank was lighter, but this happened a few months ago and I can't remember.

[kevinh 409]

The APU definitely wasn't running in-flight, and the imbalance, as I now recall, was ~800 lbs. I could be wrong, but I think I've read that the NG's APU burns approximately 4 lbs/minute. I always use the GPU at the gate, fire-up the APU just before PB, and shut it down immediately after two good engine starts. So, no, APU usage wouldn't account for the size of the imbalance.

 

Someone else asked which tank was lighter, but this happened a few months ago and I can't remember.

4 lb/min doesn't sound much, but it's 240 lb/hr and in 3 hours could result in a 720 lb imbalance. So an APU left running (easy to do, no matter how careful you may be) certainly could create this kind of imbalance.